This invention pertains to spool valves and more particularly to a four way valve including a body having a longitudinal cavity within which is a spool mounted for reciprocation longitudinally therein and having elements controlling flow of fluid between an inlet port in the body adapted for connection to a source of fluid, especially oil, under pressure, an outlet port in the body adapted to be connected to a reservoir of such fluid at a lower pressure than said source, and two flow ports adapted to supply and exhaust fluid from a fluid motor driving a Vibroseis seismic generator, the ends of the spool being driven by amplifier pistons moving in cylinders of smaller diameter than the closure or guide ends of the spool, such ends substantially sealing with said cavity.
The valve spool may reciprocate at e.g. 100 Hz to 300 Hz, with a stroke of e.g. 0.2 inch. If the spool sticks it usually galls and scores itself and the sleeve lining the body cavity, both of which are expensive to replace. To prevent such sticking, liners and sleeves of special bearing metals have been employed. Also, the spool ends have been provided with annular grooves to prevent pressure differential wall sticking and to assist in even distribution of lubricant provided by the oil whose flow is controlled by the valve. The spool has been lightened by boring out its axis, the ends of the bore then being plugged.
To prevent hydraulic lock of the spool due to accumulation of liquid in the amplifier volumes at the spool ends adjacent the drive pistons, the spool ends have been provided with diagonal bores extending from the amplifier volumes to the axial bore of the spool, the amplifier volume at one end of the spool being communicated by a port in the end cap of the body with the exterior of the body whereat is connected a pipe leading to the reservoir.
Despite all of the foregoing precautions the spools have still been subject to sticking.